The invention relates to automotive weatherstrip material. More specifically, the invention utilizes thermo-expandable microspheres to produce a microcellular structure that provides a lower weight weatherstrip material with improved surface appearance and comparable stiffness to known higher weight materials for use in the automotive industry.
Automotive weatherstrip material is generally used to create a seal between adjoining surfaces of an automobile. The seal functions to prevent environmental factors, such air, dirt, and water, from passing into a sealed portion or area of a vehicle. For example, a weatherstrip may be used to create body seals, trunk lid seals, door-to-door seals, door-to-frame seals, rocker seals, and hood seals, among others.
The automotive industry continually strives to reduce the weight of automobiles and other vehicles. This is due in part to the fact that weight affects fuel consumption which is regulated by government standards aimed at achieving reductions in fuel consumption, and thus the reduction of potentially harmful emissions. With this and other factors in mind, makers of weatherstrip materials continually work to improve their product. One effort focuses on reducing the weight of the weatherstrip material. Weight reduction, however, must be balanced with the need to preserve properties such as surface quality and stiffness, which can suffer as the weight is reduced, and particularly as the blown specific gravity, which corresponds to weight, of sponge rubber compounds approaches or drops below about 0.60 g/cc. Of particular interest herein is the desire to find new and alternative weather strip materials that provide lighter weight options, while not sacrificing the hardness, stiffness, and other desirable performance parameters of existing weatherstrip materials.
In general, automotive weatherstrips comprise a main body member and a bulb member. The main body member is that portion of the weatherstrip that is secured to at least one of a pair of abutting or adjoining surfaces. Therefore, the main body member is generally comprised of a hard, stiff material, such as a dense rubber, that resists degradation due to heat, moisture, and other environmental conditions. The bulb member is that portion of the weatherstrip that generally extends from the base member and is received in or is compressed by the second abutting or adjoining surface, i.e., it is received between two abutting and adjoining surfaces, creating a seal. Due to its function and physical position between adjoining surfaces or parts of the vehicle, the bulb member is generally comprised of a sponge-like, less dense and more resilient rubber material.
In one effort to achieve reduced weight of the overall weatherstrip, the dense rubber base portion of the weatherstrip has been formulated using blowing agents. In this regard, U.S. Pub, App. No. 2007/0084127 A1 provides an automobile weatherstrip comprising a fitting base and a bulb shape, where the fitting base is formed of dense rubber with porosity containing air bubbles obtained by mixing thermal expansion microcapsules with the dense rubber, followed by vulcanization of the mixture. This application teaches that it is important to retain the microcapsule shells intact, avoiding rupture of the same, in order to diminish the deleterious effects caused by the presence of open pores that create a rough and/or blistered surface. Use of the microcapsules is reported to reduce the specific gravity of the fitting base material from approximately 1.1 g/cc to a blown specific gravity of about 1.0 g/cc.
While the foregoing does reduce weatherstrip weight to some degree, there remains a need to reduce the weight even further. In this regard, the invention disclosed, in one embodiment, focuses on using thermo-expandable microspheres in the sponge bulb member composition or active section of an automotive weatherstrip, as opposed to the dense rubber base member or section. Manufacturers generally use chemical blowing agents in the formulation of sponge weatherstrip materials to form porosity and lower the specific gravity of sponge automotive weatherstrips. Such blowing agents include, for example, p,p′-oxybis(benzenesulphonylhydrazide)(OBSH), and/or azodicarbonamide (AZ), and other similar chemical blowing agents. The use of such materials lowers the blown specific gravity. However, properties such as surface quality and stiffness generally suffer once the blown specific gravity of the sponge bulb material compounds used in the weatherstrip formulations approach 0.60 g/cc or below. Therefore, there is a need in the automotive industry to reduce the weight of the weatherstrip by reducing the blown specific gravity of the sponge bulb member material without sacrificing hardness, stiffness or other desirable performance parameters met by known, heavier weatherstrip materials, and while yet providing a smooth and aesthetically pleasing outer surface.
It would, therefore, be advantageous to have a weatherstrip material including a sponge bulb member exhibiting a blown specific gravity of below 0.6 g/cc in conjunction with hardness and stiffness comparable to heavier materials and yet having a smooth, aesthetically pleasing appearance.